1. Field of the Invention
The present invention relates to a flow tester for testing a flow characteristic of a thermoplastic and, a strand cutting unit, a plastic sample supply unit, and cleaning unit used by the tester.
1. Related Background Art
A melt-flow characteristic of a polymer material, e.g., a thermoplastic depends on a shear rate and is thus a significant factor as an index in fabrication. Therefore, the melt-flow characteristic is standardized in JIS as "Method of Testing Flow Characteristic of Thermoplastic", JIS K 7210.
This method of testing the flow characteristic uses an extrusion type plastomer comprising a vertically supported cylinder, a piston on which a weight is mounted at an upper portion thereof and which is inserted in the cylinder, a die mounted on a lower end of the cylinder, and a heater provided to surround the cylinder. A sample of a thermoplastic is filled in the cylinder and heated by the heater to melt. Then, the molten sample is extruded from the die by the piston. A mass of the strand as the extruded material per unit time is obtained, converted to a mass extruded per 10 minutes, and determined as an MFR value.
Methods A and B are defined as methods of obtaining the mass of the strand per unit time. According to method A, a strand flowing per unit time is cut, and its mass is weighed. According to method B, a time during which a strand of a unit volume flows out is measured to calculate the mass of the strand. In either method, the test described above is repeated three times, and their average is obtained and determined as the MFR value.
In this manner, according to the method A, a strand extruded from the die is cut (sheared) three times. Conventionally, in order to cut the strand, a person who conducts the test uses a spatulate cutting member and performs cutting by sliding the cutting member along the lower end face of the die.
In the cutting operation, a strand having a high viscosity must be cut instantaneously at a predetermined timing. Therefore, in a conventional manual operation by a testing person, an individual difference occurs, or a difference between maximum and minimum values of the measurement values becomes large, making it difficult to perform an accurate measurement. In addition, the testing person needs high skill.
A tester of this type described above has a plastic sample supply unit for supplying various types of plastic samples to the plastometer prior to a test.
FIG. 1 schematically shows a conventional plastic sample supply unit. As shown in FIG. 1, this plastic sample supply unit has a sample bottle stocker 202, a bottle tilting means 203, a conveying means 204, a vibrating feeder 205, and a hopper 207. The sample bottle stocker 202 stores a multiple of sample bottles 201. The bottle tilting means 203 tilts the sample bottles 201. The conveying means 204 transfers and conveys the sample bottles 201 between the sample bottle stocker 202 and the bottle tilting means 203. The vibrating feeder 205 receives a sample Sa which pours out from the sample bottle 201 by the bottle tilting means 203. The hopper 207 receives the sample Sa supplied from the vibrating feeder 205 and guides it to a cylinder 206a of a plastometer 206. Various types of samples Sa are stored in the sample bottles 201 in advance. Each sample Sa is taken out from the sample bottle stocker 202 and transferred to the bottle tilting means 203 by the conveying means 204. The sample Sa transferred to the bottle tilting means 203 pours out onto the vibrating feeder 205 from the sample bottle 201 and is guided to the down stream hopper 207 by vibration of the vibrating feeder 205. The sample Sa guided to the hopper 207 is collected by a taper portion 207a of the hopper 207 and is filled in the cylinder 206a of the plastometer 206 through a tube 207b continuous with the taper portion 207a. Then, the sample Sa filled in the cylinder 206a is sufficiently rammed by a rammer 208 to prevent bubbles from being generated in the sample Sa.
In this manner, in a conventional plastic sample supply unit, when an adherent sample or a powder type sample is to be handled, the sample Sa can easily adhere to the inner circumferential surface of the sample bottle 201. Even when the sample bottle 201 is tilted, the sample Sa sometimes does not completely pour out and remains in the sample bottle 201. Since the tube 207b portion of the hopper 207 is arcuated, the sample Sa can clog in the arcuated portion to cause a so-called bridge, and the sample Sa may not be completely supplied to the plastometer 206.
In addition, the sample remaining on the inner surface of the hopper is mixed in a sample of a subsequent test to denature it. Therefore, conventionally, a continuous automatic operation of the tester is stopped, and the operator manually cleans the hopper and the rammer.
Such a cleaning operation is cumbersome and takes longer time than an actual test does, thus prolonging the entire operation time required for the test. Also, during the cleaning operation, the residual sample is scattered in the air to contaminate the periphery of the tester.